You can get reconditioned vacuum pumps to run a aeration system on ebay all day long from 45-75 bucks. I have 2, one is a spare. Paid 110 for 2. Air hose is cheap and I bought 2 diffusers online for less than 20 each. I also have a cheap timer and I run mine about 10 hours a day, 5 around noon and 5 around midnight. I think 350 is high for a DIY setup, especially when using equipment not designed for the task and probably not as efficient in the long run. The point of the aeration system is to turn your pond over and if you are not doing that then the pond can still stratify. That being said I hope your system treats you and your pond right for many years to come.
tz
